Babylonian Talmud, Baba Batra 21b

R. Huna said: If one of the inhabitants of an alley establishes a handmill there, and another one comes to do the same, the law gives the former the right to prevent the latter; for the former may claim: "You are cutting off my livelihood." He is supported by the following: Fishermen must remove their nets from a fish which has already been marked by one of them while it was trying to escape from him to a distance that a fish is usually able to traverse. And to the question, How far is it? Rabba b. R. Huna said: "The distance of a parsa"? Nay, with fish the case is different, as they place spies (to look out for bait, and the former fisherman is certain that the fish will go to his bait and then he will surely catch it; but here his comrade may say to him: "I am not injuring your livelihood, as your customers will go to you and mine to me"). [Soncino translation]